'''
难度：简单
请实现一个函数，把字符串 s 中的每个空格替换成"%20"。
示例 1：
输入：s = "We are happy."
输出："We%20are%20happy."
'''
class Solution:
    def replaceSpace(self, s: str) -> str:
        res = []
        for ch in s:
            if ch == " ":
                res.append("%20")
            else:
                res.append(ch)
        return ''.join(res)